Olefin is a type of unsaturated hydrocarbon that contains a carbon-carbon double bond. There are several synonyms for the word "olefin", which include alkene, polyethylene, polypropylene, and propene. Alkene is a general term that refers to any hydrocarbon that contains a carbon-carbon double bond, whereas the terms polyethylene and polypropylene refer to specific types of olefin polymers. Propene is a specific type of olefin that is also known as propylene. The use of these synonyms can be helpful when discussing olefins in different contexts, such as in the plastics industry or in organic chemistry research.